Cognitive radio is a form of wireless communication in which radios alter the radio resources they use based on local radio network conditions. Radio resources with a locally low utilization ratio are identified and taken into use. That is, a transceiver can detect which communication channels are in use and which are not, and use the vacant channels while avoiding occupied ones. In this way better spectrum efficiency can be achieved as compared to static allocation of channels.
One of the technical solutions needed for cognitive radio is how to identify the local radio network conditions. For example, in order to support hierarchical primary-secondary spectrum usage scenarios, cognitive radios should be able to detect a primary (legacy) user at a low power level and avoid causing interference to it. Spectrum sensing is a basic functionality used for detecting local radio network conditions. Spectrum sensing can be used for detecting primary users and finding unoccupied or underutilized spectrum. Also, spectrum sensing can be used to measure utilization degree and dynamics of frequency bands of interest.
Oliver Holland, Alireza Attar, Nikolas Olaziregi, Nima Sattari, and A. Hamid Aghvami, “A Universal Resource Awareness Channel for Cognitive Radio”, the 17th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC'06) proposes a concept of a universally available Resource Awareness Channel for conveying information about resource usage for cognitive radio. Therein nodes transmit over a dedicated channel information about the resources that are used by the traffic that they are receiving. Other nodes then listen to this channel and thereby receive information about interference conditions in the system.
US20080171552 provides a communication method for a distributed network system where cognitive radio technology is used.